This invention relates to an integrated circuit device comprising a circuit element, such as a random logic, a memory, and others, and a test circuit for the circuit element. Therefore, the circuit element will be called a main circuit.
Recently, remarkable improvements have been made in the integration of circuit devices. As a result, a large number of main circuits can be mounted on a single integrated circuit device, such as a circuit element.
It is a matter of course that the integrated circuit device be subjected to various tests after its manufacture. One of these tests is an AC test, which is well known in the art.
The AC test is generally carried out on the integrated circuit device as a whole, and will be referred to hereunder as the whole AC test. In addition, the AC test is often carried out on each of the main circuits and will, thus, be an individual AC test. The individual AC test is strongly required in particular case where the memory is mounted as one of the main circuits on the integrated circuit device. This is because it is difficult in this particular case to carry out the whole AC test with a high efficiency.
A conventional integrated circuit device comprises paths from the test pads, which are junctions between the inside and outside of the integrated circuit device to the main circuits. In order to carry out the individual AC test, a test unit is connected to the test pads. The test unit is for producing a test signal and for analyzing the output signals produced by each of the main circuits. More particularly, the test signal is supplied as an input signal to a selected one of the main circuits through one of the test pads. Responsive to the test signal, the selected main circuit produces an output signal. The output signal is supplied back to the test unit through another one of the test pads.
However, the integrated circuit device has various disadvantages.
(a) the test unit order to produce the test signal and to analyze the output signal is complicated and expensive.
(b) inasmuch as the test and output signals are transmitted through the paths from the main circuits under test to test pads, additional capacitance is added to the main circuits under test.
(c) it is unavoidable to make the integrated circuit device large in size, since the paths from the main circuits under test to the test pads take up a large area in the integrated circuit device.